linux-kernel - Re: [PATCH v6 3/7] x86/mm: Use 'ptdesc' when freeing PMD pages

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Message-ID: <bf6ee535-cd5c-41ed-b0a0-f2dc10c1382d@linux.intel.com>
Date: Wed, 15 Oct 2025 13:19:44 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Kevin Tian <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...dia.com>,
 Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Alistair Popple <apopple@...dia.com>,
 Peter Zijlstra <peterz@...radead.org>, Uladzislau Rezki <urezki@...il.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Andy Lutomirski <luto@...nel.org>, Yi Lai <yi1.lai@...el.com>,
 David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>,
 Mike Rapoport <rppt@...nel.org>, Michal Hocko <mhocko@...nel.org>,
 Matthew Wilcox <willy@...radead.org>
Cc: iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v6 3/7] x86/mm: Use 'ptdesc' when freeing PMD pages

On 10/15/25 07:19, Dave Hansen wrote:
> On 10/14/25 06:04, Lu Baolu wrote:
>> -#if defined(CONFIG_SPLIT_PMD_PTLOCKS)
>> -
>> +#if defined(CONFIG_SPLIT_PMD_PTLOCKS) || defined(CONFIG_X86_64)
> 
> What's with the #ifdef munging? It's not mentioned in the changelog.
> 
> I went looking at this because pmd_free_pte_page() is right in the
> middle of the action on this reported use after free:
> 
>> https://lore.kernel.org/all/68eeb99e.050a0220.91a22.0220.GAE@google.com/
> 
> so something fishy is going on. It would be great to narrow that report
> down to a _specific_ patch in the series.

Yes. I am trying to reproduce the issue on my local machine and then
narrow down the reported issue.

Thanks,
baolu